1. Field of the Invention
The present invention is directed to a method for locating an examination site for conducting a diaphanoscopic examination of a living subject, as well as to an apparatus for implementing the method.
2. Description of the Prior Art
In the framework of diaphanoscopic examinations, a region of a living subject to be examined is transilluminated with light and the transillumination image that is registered is utilized for diagnosis. If one wishes to detect a pathologically induced, optical change in a specific, transilluminated volume of the life form and make the result available as the basis of the diagnosis, then the selection of an "optimum" irradiation site must assure that the pathologically modifiable tissue penetrated by the photons is maximum compared to the pathologically constant volume in order to thus be able to actually examine the region of maximum information in the scope of the main examination. This is especially important when the pathological change to be detected is small. A diaphanoscopic examination method can, for example, be implemented at a finger joint in order to make a diagnosis with regard to rheumatoid arthritis. In simplified terms, a finger joint is composed of bone tissue, cartilage tissue, skin tissue and capsular tissue as well as joint fluid. The bone tissue, cartilage tissue as well as the surrounding skin tissue thereby remain pathologically constant in the early stage; the possible pathological changes occur only in joint capsule as well as the joint fluid. In order to obtain a maximum informational content with respect to this relatively narrow diagnostic volume in the framework of the main examination, it is necessary to implement the transillumination at the optimum examination site, so that the informational content that is obtained is as great as possible. The term examination location (or examination) being a tissue location prescribable on the basis of a position value, this being illuminated by the beam crossection of the light source employed for the examination.
U.S. Pat. No. 5,452,723 discloses a spectroscopy method that is utilized in conjunction with spectroscopy of human tissue. With the method disclosed therein, the distortions of the obtained measured values are to be corrected given an examination of a thick tissue several millimeters thick due to the increased number of dispersion centers of the thick tissue compared to the spectroscopy of a very thin tissue only a few micrometers thick wherein fewer dispersion centers that influence the measured result are established. This ensues such that a spectrum of the diffuse reflectance is registered first, followed by the spectrum to be "distortion-corrected", for example the fluorescence spectrum. An effective reflectance function is subsequently determined based on probability functions. The distortion-corrected fluorescence spectrum is then determined by dividing the registered fluorescence spectrum by the effective reflectance spectrum described on the basis of the effective reflectance function. The distortions of the spectrum of the thick tissue deriving from dispersion and absorption effects as well as the geometrical and the boundary surface conditions are eliminated, the spectrum curve that is obtained corresponds in good approximation to that of a thin tissue. The "distortion-corrected" measured curve that is obtained is subsequently compared to known reference curves, and the best fit curve is identified, this being subsequently investigated in view of the presence and concentration of reference fluorophores, which is the basis for the diagnosis of the corresponding tissue property.